Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is etiologically linked with KS, primary effusion lymphomas (PELs) and multicentric Castleman's disease. These diseases occur in AIDS and in other patients and current therapies are limited. KSHV latently infects the vast majority of tumor cells and viral DNA persists as a multiple copy, extrachromosomal, circular episome. To persist in proliferating cells, episomes must replicate and efficiently segregate to daughter nuclei. KSHV latency associated nuclear antigen (LANA) binds terminal repeat (TR) DNA to mediate KSHV episome persistence. LANA mediates TR DNA replication and binds TR DNA to tether episomes to mitotic chromosomes for efficient segregation to progeny nuclei. LANA is essential for KSHV episome maintenance and central to viral latency. The N- and C-terminal regions are essential for LANA function and bind mitotic chromosomes and TR DNA. However, the role(s) of internal domains in LANA mediated episome maintenance are unknown. We have now identified a 68 amino acid internal LANA region which exerts a critical effect on episome maintenance. We have also found that poly(ADP-ribose) polymerase-1 (PARP1) exerts a potent inhibitory effect on LANA mediated episome persistence. Small molecule inhibitors of LANA function would be powerful tools to probe LANA function and viral latency and would provide new therapeutic strategies. However, currently, no such inhibitors have been identified or developed. This work will address critical aspects of LANA biology. The newly identified internal LANA region critical for episome maintenance will be investigated, including its mechanism of action. Such knowledge will provide insight into the basic mechanisms of LANA mediated episome persistence. The biology of PARP1 inhibition of episome maintenance will be investigated. Study of this area is critical since PARP1 appears to be a key component of the host response to KSHV infection. Small molecule inhibitors of LANA function will be identified. These compounds will provide novel probes of KSHV latency and serve as potential therapeutic and preventive agents for KSHV malignancy.